The present invention in related to the field of control scheduling and, more particularly, to the field of smoothly changing between different control modes.
Human transport devices serve to move a person over a surface and may take many different forms. For example, a human transport device, as the term is used herein, may include, but is not limited to, wheelchairs, motorized carts, bicycles, motorcycles, cars, hovercrafts, and the like. Some types of human transport may include stabilization mechanisms to help ensure that the device does not fall over and injure the user of the transport device.
A typical four-wheeled wheelchair contacts the ground with all four wheels. If the center of gravity of the combination of the wheelchair and the user remains over the area between the wheels, the wheelchair should not tip over. If the center of gravity is located above and outside of the ground contacting members of the transport device, the transport device may become unstable and tip over.
Referring now to FIG. 1A, a typical wheelchair 100 is shown. The wheelchair 100 and the user 102 define a frame. The frame has a center of gravity 104 located at a position vertically disposed above the surface 106. The term xe2x80x9csurfacexe2x80x9d as it is used herein shall refer to any surface upon which a human transport device may sit. Examples of a surface include flat ground, an inclined plane such as a ramp, a gravel covered street, and may include a curb which vertically connects two substantially parallel surfaces vertically displaced from one another (e.g., a street curb).
The surface 106 may be at an incline as compared to the horizontal axis 108. The angle by which the surface 106 is offset from the horizontal axis 108 shall be referred to herein as the surface pitch and will be represented by an angle denoted as xcex8s.
The front wheel 112 and the rear wheel 110 of the wheelchair 100 are separated by a distance d. The distance d between the two wheels may be measured as a linear (e.g., straight line) distance. If the center of gravity 104 of the system is located at a position above and between the two wheels, 110 and 112, the wheelchair 100 should remain upright and relatively stable. The wheels 110 and 112 typically have opposing counterparts (not shown) on the other side of the wheelchair. The opposing counterparts may each share an axis with wheels 110 and 112, respectively. The area covered by the polygon which connects the points where these four wheels touch the ground (or the outside portions of the ground contacting parts, when the ground contacting part may cover more than a point) provides an area over which the center of gravity 104 may be located while the wheelchair remains stable. In various places in this discussion below this area may be referred to as the footprint of the device. The footprint of a device, as the term is used herein, is defined by the projection of the area between the wheels as projected onto the horizontal plane. If the center of gravity is above this location, the transport device should remain stable.
If the center of gravity 104 is vertically displaced above the surface 106 and outside the footprint (i.e., the projection of area between the wheels 110 and 112 onto the horizontal plane), the stability of the wheelchair 100 may decrease and the wheelchair 100 may tip over. This could happen, for example, when the wheelchair is on a surface that has a steep incline. When on a steep incline, the center of gravity 104 may shift back and cause the wheelchair 100 to flip over backwards. This is shown in FIG. 1B where the center of gravity 104 is located at a position that is outside the footprint of the wheelchair 100. The center of gravity 104 is shown including a gravity acceleration vector (g) which linearly translates the center of gravity 104 in a downward direction. The wheelchair 100 may rotate about an axis of the rear wheel 110 until the wheelchair 100 contacts the surface being traversed.
The user 102 may help to return the center of gravity 104 to a location that is above the area between the wheels 110 and 112 by leaning forward in the wheelchair 100. Given this limited control of the location of the center of gravity 104, it is clear that human transport devices such as wheelchairs may encounter great difficulties when traversing uneven surfaces such as a curb or steps.
Other types of human transport devices may include control mechanisms which allow the transport device to balance on two wheels. The two wheels may be connected to a single3 axis that passes through the center of the wheels. The axis connects the wheels in such a manner that the forward and backwards motion of the device is perpendicular to the axis. The control mechanisms may keep the device and the user in a stable upright position by driving the wheels forwards and backwards to keep the center of gravity located over the wheel axis. Such devices may additionally provide for locomotion by allowing the center of gravity to be displaced by a distance forward or backwards from wheel axis and having the wheels rotate in order keep the center of gravity located at that position. Examples of such devices are disclosed in U.S. Pat. Nos. 5,701,965 and 5,719,425 which are hereby incorporated by reference.
According to embodiment of the present invention, a system of converting between a first operating mode and a second operating mode in a device is disclosed. In this embodiment, the system includes a control loop which utilizes gain coefficients associated with the first operating mode to control the system in the first operating mode and utilizes gain coefficients associated with the second operating mode when operating in the second operating mode. In this embodiment, the system also includes a gain selector which causes the control loop to operate using the coefficients associated with the second operational mode at substantially the same instant that the device transitions from the first operational mode to the second operational mode.
According to another embodiment of the present invention, a method of smoothly operating a device that is responsive to a control signal is disclosed. In this embodiment, the method includes steps of determining a value for the control signal, processing the control signal to create a modified control signal, and applying the modified control signal to the device.
In another embodiment of the present invention, a method of smoothly switching between modes in a multi-modular apparatus is disclosed. In this embodiment, the method includes steps of determining whether a mode change has occurred, and determining an offset value if the mode has changed. In this embodiment, the method also includes steps of adding a decaying version of the offset value to a control signal before the control signal is applied to the apparatus to create a smoothed control signal, and applying the smoothed control signal to the apparatus.